Continuum Robots for Medical Applications: A Survey

Traditional rigid robot application in the medical field is limited due to the limited degrees of freedom caused by their material and structure. Inspired by trunk, tentacles, and snakes, continuum robot (CR) could traverse confined space, manipulate objects in complex environment, and conform to curvilinear paths in space. The continuum robot has broad prospect in surgery due to its high dexterity, which can reach circuitous areas of the body and perform precision surgery. Recently, many efforts have been done by researchers to improve the design and actuation methods of continuum robots. Several continuum robots have been applied in clinic surgical interventions and demonstrated superiorities to conventional rigid-link robots. In this paper, we provide an overview of the current development of continuum robots, including the design principles, actuation methods, application prospect, limitations, and challenge. And we also provide perspective for the future development. We hope that with the development of material science, Engineering ethics, and manufacture technology, new methods can be applied to manufacture continuum robots for specific surgical procedures.

In this paper, we examine key issues underlying the design and operation of robots featuring continuous body (“continuum”) elements. We contrast continuum and continuum-like robots created to date with their counterparts in the natural world. It is observed that natural continuum locomotors or manipulators almost invariably rely on hard or discrete elements (in their structure or operation) in their interactions with their environment. We suggest innovations in continuum robot design and operation motivated by this observation, supported by experiments using the “Tendril” continuum robot. The results suggest new ways in which continuum robot operations could be significantly enhanced. In particular, the exploitation of “hard” and “discrete” environmental features can greatly enhance stability in continuum robot operations, compensating for inherent backbone compliance. Additionally, the incorporation of discrete behaviours (sweeping and striking with the backbone) can both compensate for imprecision in continuum robot control and enable new impulsive manipulation modes. We discuss the implications for the creation and potential application of novel hybrid continuum and discrete robots.

Continuum or hyper-redundant robot manipulators can exhibit behavior similar to biological trunks, tentacles, or snakes. Unlike traditional rigid-link robot manipulators, continuum robot manipulators do not have rigid joints, hence these manipulators are extremely dexterous, compliant, and are capable of dynamic adaptive manipulation in unstructured environments. However, the development of high-performance control algorithms for these manipulators is quite a challenge, due to their unique design and the high degree of uncertainty in their dynamic models. In this paper, a controller for continuum robots, which utilizes a neural network feedforward component to compensate for dynamic uncertainties is presented. Experimental results using the OCTARM, which is a soft extensible continuum manipulator, are provided to illustrate that the addition of the neural network feedforward component to the controller provides improved performance.

Applications of continuum robot in the field of robotics facility have been advancing at a staggering pace due to their flexibility. The ability to control the continuum robot remotely and efficiently would be beneficial for many practical case, for example usage in narrow space, endoscopic and minimally invasive surgical procedures application. The ability to glide through complex curvilinear pathways makes it ideally suitable to be used with solar cell application as it could offer the movement that can follow the sun motion. This could enhance the efficiency of energy transformation of the solar cell as optimum radiation distance could be obtained. In this paper, the design of continuum robot with motion control to be used as solar cell installation supporting structure would be discussed. The continuum robot movement is controlled by an elastic backbone-liked structure. The controller is designed for closed loop control using Arduino programming. The effect of solar cell weight on the top with the maximum of 3 kg is considered. The structure movement required include bending, rotating, extension and compression. The research results showed that the designed system has a potential to be used as a solar cell installation support with smooth motion.

A twisting problem is identified from the central located flexible backbone continuum robot. Regarding this problem, a design solution is required to mechanically minimize this twisting angle along the backbone. Further, the error caused by the kinematic assumption of previous works is identified as well, which requires a kinematic solution to minimize. The scope of this paper is to introduce, describe and teste a novel design of continuum robot which has a twin-pivot compliant joint construction that minimizes the twisting around its axis. A kinematics model is introduced which can be applied to a wide range of twin-pivot construction with two pairs of cables per section design. And according to this model, the approach for minimising the kinematic error is developed. Furthermore, based on the geometry and material property of compliant joint, the work volumes for single/three-section continuum robot are presented, respectively. The kinematic analysis has been verified by a three-section prototype of continuum robot and adequate accuracy and repeatability tests carried out. And in the test, the system generates relatively small twisting angles when a range of end loads is applied at the end of the arm. Utilising the concept presented in this paper, it is possible to develop a continuum robot which can minimize the twisting angle and be accurately controlled. In this paper, a novel design of continuum robot which has a twin-pivot compliant joint construction that minimizes the twisting around its axis is introduced, described and tested. A kinematics model is introduced which can be applied to a wide range of twin-pivot construction with two pairs of cables per section design. Furthermore, based on the geometry and material property of compliant joint, the work volumes for single/three-section continuum robot are presented, respectively. Finally, the kinematic analysis has been verified by a three-section prototype of continuum and adequate accuracy and repeatability tests carried out.

Continuum robots have seen increased utilization in various fields such as aerospace, rescue operations, human interaction, and especially medicine. More specifically, in medicine, continuum robots have enabled minimally invasive surgeries and faster patient recovery time. However, the design of continuum robots needs to be improved, especially by enhancing or incorporating characteristics that improve functionality across various applications. This paper explores different mechanisms, including bistable, compliant, and lamina emergent mechanisms, to achieve these design goals. Specifically compliant bistable mechanisms which can store energy when deformed and utilize this energy to transition from one state to another have shown significant promise for the design of continuum robots. In this paper we explore the characteristics and functions associated with compliant bistable mechanisms and their potential integration in device designs, we review the design process for adapting compliant bistable mechanisms to continuum robots, highlighting the challenges and considerations involved. We also present two examples of applications to continuum robot designs that demonstrate the potential of compliant mechanisms for creating varied functionality for a number of applications. By understanding the capabilities and limitations of compliant mechanisms, we can advance the design of continuum robots, which presents a significant opportunity for innovation and progress in the field of medical device design.

Continuum or hyper-redundant robots are robots which exhibit behavior similar to biological trunks, tentacles and snakes. Unlike traditional robots, continuum robot manipulators do not have rigid joints, hence the manipulators are compliant, extremely dexterous, and capable of dynamic, adaptive manipulation in unstructured environments; however, the development of high-performance control algorithms for these manipulators is a challenging problem. In this paper, we present an approach to whole arm grasping control for continuum robots. The grasping controller is developed in two stages; high level path planning for the grasping objective, and a low level joint controller using a neural network feedforward component to compensate for dynamic uncertainties. These techniques are used to enable whole arm grasping without using contact force measurements and without using a dynamic model of the continuum robot

In recent times, the role of minimally invasive surgery (MIS) in diagnosis and therapy has significantly increased. The rapid adoption of MIS can be attributed to the considerable benefits offered to patients. This includes reduced patient trauma, less scarring and faster recovery times. Furthermore, the reduced patient trauma enables the treatment of high-risk patients who were initially denied surgery. However, restricted access, reduced visibility and limited dexterity of instruments at the treatment location are among the challenges of MIS. Hence, the demand for new technology such as continuum robots that can assist the clinician during MIS is significant. Potentially, the control of continuum robots such as flexible needles, delivery sheaths and steerable catheters could be used to address challenges associated with MIS. In this thesis, closed-loop control methods using flexible needles, delivery sheaths and steerable catheters for percutaneous and cardiovascular interventions are developed. The closed-loop control methods are used to accurately position the continuum robot at the treatment location and to provide instrument tip stabilization for tissue motions. Feedback of the continuum robot and target location for closed-loop control is provided by ultrasound images and electromagnetic tracking. The closed-loop control methods (aided by path planning) uses continuum robot models for the accurate positioning and stabilization of the instrument tip. Furthermore, the control input is provided to actuators and mechanisms in order to steer the continuum robot. In order to evaluate the closed-loop control of continuum robots, an experimental testbed is developed and used to reproduce a clinical environment. The proposed closed-loop control methods for continuum robots are evaluated in clinically-relevant experiments. The results obtained from experiments showed an improved continuum robot tip positioning compared to clinical practice. In order to avoid sensitive tissue that could be present in surgery, it is demonstrated that constraints integrated in the control method could be used to restrict the instrument motion. Furthermore, stabilization of the continuum robot tip for tissue motions is demonstrated. However, the proposed closed-loop control method for continuum robots could benefit from improvements in feedback, control methods, continuum robot design, and instrument steering mechanisms with actuators. Therefore, with modifications, the proposed methods could be successfully deployed in clinical practice.

Continuum (continuous backbone) robots are suitable for operation in unstructured environments thanks to their inherent compliance. They can adjust their shape to navigate through complex environments and grasp a wide variety of payloads with their compliant backbones. However, controller design for continuum robots is challenging due to their complex dynamics. In this paper, we introduce a new and novel strategy for trajectory control of continuum robot sections. The approach is based on a virtual discrete-jointed robot whose degrees of freedom are directly mapped to those of a continuum robot section. A conventional control strategy is developed for the virtual robot, for which inverse kinematics and dynamic equations are formulated and exploited, with appropriate transformations developed for implementation on the continuum robot. Simulations of the virtual robot computed torque control were executed and results indicate that the control method has good trajectory tracking performance. The control algorithm was implemented on a three degree of freedom section of the OctArm continuum manipulator, with decent tracking performance (steady state tracking error of merely 3mm during extension).

The design and analysis of continuum robots have consistently been a prominent research focus in the field of mechanics. However, portable continuum robots with minimal spatial occupancy, which have great potential for applications such as search and rescue, are scarcely available. This paper presents a novel helical-coiled multi-segment flexible continuum robot featuring helical deployment and compact design, with an integrated framework for structural design, kinematic modeling, and experimental validation. The design of the helical-coiled multi-segment flexible continuum robot for unstructured environment detection, including a flexible body, an actuation module, a feed module, and a sensing module, is presented systematically. Kinematic models of both single- and multi-segment continuum robots were established based on the constant curvature model to analyze the parameter mapping relationship from the end-effector position and orientation to the driving inputs. Furthermore, the feedforward motion of the robot was examined, and an uncoiling strategy based on S-curve compensation was employed to complete the kinematic analysis. Finally, the accuracy of the kinematic model considering the active uncoiling feed motion was validated through experimental analysis, demonstrating the motion characteristics of the continuum robot. Altogether, this study provides a framework for the design and analysis of helical-coiled continuum robots.

Compliant joints are widely used in the structural design of 3D-printed continuum robots as their monolithic structure can greatly simplify the assembly process. However, some highly flexible compliant joints, such as the leaf-spring joints, still suffer from unstable rotation centers when interfered by external forces, which greatly reduces the motion stability of the constructed continuum robots. To cope with this problem, we propose a topology-optimization-based method in this paper to achieve efficient structural design of the complaint joints in continuum robots. With our method, the rotation stability of compliant joints can be improved without causing stress concentration problems. Experiments were also carried out to evaluate the bending performance of the 3D-printed continuum robots equipped with optimized compliant joints. Results demonstrated that, compared to continuum robots with the conventional leaf-spring joints, the optimized robots showed much less twisting deformation caused by out-of-plane loads, which exhibited the high rotation stability of the optimized joints. In future work, the proposed method can be further developed to achieve optimization of other mechanical properties of the compliant joints in continuum robots.

The increasing demand for multi-degree-of- freedom (DOF) continuum robot in presence of highly nonlinear dynamic parameters in a number of industries has motivated a flurry of research in the development of soft computing nonlinear methodology. This research contributes to the on-going research effort by exploring alternate methods for controlling the continuum robot manipulator. This research addresses two basic issues related to the control of a continuum robots; (1) a more accurate representation of the dynamic model of an existing prototype, and (2) the design of a robust feedback controller. The robust back stepping controller proposed in this research is used to further demonstrate the appealing features exhibited by the continuum robot. Robust feedback controller is used to position control of continuum robot in presence of uncertainties. Using Lyapunov type stability arguments, a robust back stepping controller is designed to achieve this objective. The controller developed in this research is designed into two steps. Firstly, a robust stabilizing torque is designed for the nominal continuum robot dynamics derived using the constrained Lagrangian formulation. Next, the fuzzy logic methodology applied to it to solution uncertainty problem. The fuzzy model free problem is formulated to minimize the nonlinear formulation of continuum robot. The eventual stability of the controller depends on the torque generating capabilities of the continuum robots. Index Term — Back stepping control methodology, fuzzy inference system, continuum robot manipulator, robust control.

Introduction. An important area of application of advanced information technologies is intelligent control of dynamic objects in complex environment. The purpose of the article is to analyze and generalize theoretical as well as practical results related to elaboration of systems for intelligent control of dynamic objects. Future research prospects in this area are also outlined. Methods. Methodological tools include theories of intelligent control, decision making, artificial intelligence, computer vision, system analysis, acoustics, problem solving, conflict resolution. Results. The article outlines main results related to intelligent control of dynamic objects in complex and changing environment. Issues of system integrity, distinctions between traditional and intelligent control, usage of artificial intelligence in autonomous systems, data structuring, image comprehension of current situation have been discussed. Information about the implementation of high-precision control systems for various kinds of dynamic objects (sea vessels, aircrafts, UAVs) in the conditions of conflicts as well as essential informational restrictions has been presented. Though the article covers a wide spectrum of research activities with a considerable period, the authors tried to stress both interconnections and succession of scientific as well as technological achievements in the examined area. Conclusions. Main directions of future research include development and implementation of new approaches to the increase of intellectualization level for information technologies and systems.

Continuum robots are highly miniaturizable, exhibit non-linear shapes with several curves, and are flexible and compliant. In particular, concentric-tube and tendon-driven continuum robots can be designed on a small scale with diameters of below 10 mm. A small diameter-to-length ratio enables insertion of these robots through small entry points in order to reach hardly accessible regions by avoiding obstacles. This scenario can often be found in minimally invasive surgery and technical inspections. However, to reach the target region, a deployment along a narrow tortuous path is often required. Common tendon-driven continuum robots are intrinsically incapable of such deployment and concentric-tube continuum robots require special path conditions and intensive parameter optimization. Other proposed robot types, such as hyper-redundant and pneumatically actuated robots, exhibit less favorable diameter-to-length ratios and are thus not suitable for those tasks. Since the limiting factors are found in the design of continuum robots, we propose a novel tendon-driven continuum robot design, which features an additional degree of freedom in each robot section. The backbone is composed of straight, concentrically arranged tubes, each of which composes a section and is used to adapt its length. We present a three-section continuum robot prototype with a diameter of 7 mm, determine its follow-the-leader capabilities theoretically, and validate the results experimentally using model-based control. For our 165 mm long robot prototype, the repeatability is below 2.38 mm. The model accuracy reaches a median of 3.16% over 25 configurations with respect to robot length. The path-following error over five curvilinear paths results in median errors of 2.59% with respect to robot length.

Continuum robots, owing to their inherent compliance, have become essential in endoscopic surgical procedures, such as mucosal ablation. However, the prevalent design of endoscopic manipulators, which typically features only a single active bending segment, often results in limited dexterity and accessibility. Additionally, the incorporation of variable stiffness in these robots has attracted significant interest, with the aim to improve manipulation capabilities in confined spaces. In the paper, we propose a novel variable-length continuum robot with variable stiffness for endoscopic surgery. The robot’s stiffness can be altered either by modifying the catheter’s length or solid-liquid transition of low-melting-point alloy (LMPA). The design and fabrication methods of the robot are meticulously detailed. Additionally, a quasi-static stiffness model along with a learning-based stiffness compensation approach for accurate stiffness estimation are proposed. Leveraging this model, a contact force controller is designed for ablation procedure. The experimental results show that our robot possesses good flexibility and accessibility, making it highly adept at manipulating in confined spaces. Its variable stiffness feature significantly enhances its ability to counteract external disturbance and prevent tip deformation (with a average position change of 1.1mm). Finally, through force control experiments and a surgical demonstration in a gastrointestinal model, we have further validated the robot’s applicability in surgical contexts. Note to Practitioners—This paper proposed a variable-length continuum robot with variable stiffness for endoscopic surgery. The robot can achieve axial elongation and omnidirectional bending motion, having better dexterity and accessibility than traditional medical continuum robots with one active bending segment. The robot’s stiffness can be adjusted by the length changes or solid-liquid transition of low-melting-point alloy (LMPA). Besides, an accurate stiffness model and a contact force controller are proposed for endoscopic ablation surgery. By experimental results, the robot shows high flexibility and accessibility, allowing access to confined spaces for manipulation, and good control accuracy and variable stiffness capability for endoscopic surgery.